Field of the Invention
The present invention relates generally to a device for radially tensioning movable jaws of a chuck of a machining tool and, more particularly to such a device for fixedly positioning the jaws of the chuck for machining the jaws to fit a given workpiece.
Description of the Prior Art
Conventional machine tools, such as lathes, and the like, usually include a chuck having at least two radially movable permanent jaws and means for adjusting the radial position of the jaws. While the usual permanent jaws of the machining tool may be used to grip most workpieces, the necessity often arises for a set of jaws with inner gripping faces that are accurately machined to fit a workpiece of a specific diameter. This is especially true in close tolerance work. In such an event soft jaws either replace or are attached to the permanent jaws and thereafter are machined by a cutting tool to form the accurately curved and centered gripping faces.
However, in order to machine the soft jaws, the jaws must be rigidly immobilized with the inner faces of the soft jaws accessible to the cutting tool. Rigid immobilization of the jaws cannot be achieved by the conventional jaw adjusting mechanism on the chuck due to the play or backlash of the jaw adjustment mechanism. Consequently, one previous method of machining the soft jaws has included placing a thin spacer at the inner axial end of the jaws and thereafter clamping the jaws onto the spacer to thereby eliminate the play of the jaw adjustment mechanism.
Due to the difficulty of obtaining an appropriately sized spacer. M. A. Riehart in his U.S. Pat. No. 3,104,474 which issued on Sept. 24, 1963, discloses an adjustable spacer for setting the chuck jaws of a lathe. Other similar devices have also been previously known but to my knowledge, all have been disposed inside the jaws with the backlash removed by tightening the jaws down onto the device.
These previously known devices, adjustable or otherwise, suffer several disadvantages unknown to the present invention. One such disadvantage is that the previously known devices are somewhat difficult to use in operation. In particular, the device must be precisely centered within the chuck and in addition must lie precisely in a radial plane of the chuck.
A still further disadvantage of these previously known devices is that although the spacer is placed at the inner axial end of the jaws, the device nevertheless interferes with the machining tool used to machine the soft jaws. For example, if the machining tool is extended too far into the chuck jaws the machining tool would contact and displace the device. In such an event the jaws would no longer be rigidly immobilized and the cutting tool would badly damage the soft jaws.
Also since a portion of the inner surface of the jaws is engaged by the device, this portion of the jaws cannot be machined and in close tolerance work or in applications where the workpiece must extend quite far into the chuck, this interferes with the accuracy.